• Ari Han, Dae Young Yoon, Suk Ki Chang, Kyoung Ja Lim, Byung-Moon Cho, Yoon Cheol Shin, Sam Soo Kim, and Keon Ha Kim.
• Department of Radiology, Kangdong Seong-Sim Hospital, Hallym University College of Medicine, Seoul, Republic of Korea.
• Acta Radiol. 2011 Oct 1; 52 (8): 889-93.

BackgroundComputed tomography angiography (CTA) is increasingly used for non-invasive imaging of the cerebrovascular diseases.PurposeTo evaluate the accuracy of CTA in the assessment of the variation of the segment calibers of the circle of Willis.Material And MethodsOne hundred and 17 patients with acute SAH (51 men and 66 women, mean age 50.9 years) who underwent CTA using a 16 detector-row CT scanner and DSA were evaluated retrospectively. The CTA and DSA studies were performed within 24 h after the onset of symptoms and within 24 h of each other. A total of 819 arterial segments (A-comA, right and left A1 segment, right and left P-com A, and right and left P1 segment) of the circle of Willis were determined to be aplastic (grade 1), hypoplastic (grade 2), or normal-sized (grade 3) by blinded observers evaluating CTA volume-rendered images. The CTA results were then compared with findings on the corresponding DSA images (reference standard).ResultsThe overall agreement between CTA and DSA was 92.4%. We had 62 (7.6%) cases of disagreement (58 cases of under-estimation and four cases of over-estimation by CTA) between tow modalities. The sensitivity and specificity of CTA in the detection of aplastic and normal-sized segments were more than 90%. In contrast, subgroup analysis of the hypoplastic segments showed a sensitivity of 52.6% and a specificity of 98.2%.ConclusionCTA is highly accurate in the assessment of anatomical variations of the circle of Willis; however, its sensitivity is limited in depicting hypoplastic segments.

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